ggtype

Type-safe bidirectional RPC with automatic validation and full TypeScript inference.

ggtype is a high-performance TypeScript library for building type-safe communication between client and server. Define your API once, get automatic runtime validation, full type inference, and bidirectional RPC—all with zero code generation.

What problem does this solve?

• Type safety without duplication — No need to maintain separate types for client and server. Define once, use everywhere with full inference.
• Runtime validation that matches your types — Automatic validation using AJV ensures your runtime data matches your TypeScript types.
• Bidirectional RPC with validation — Server can call client actions (and vice versa) with full type safety and validation on both sides.

When should I use ggtype?

✅ Use ggtype when:

• You're building a full-stack TypeScript application
• You want type-safe API calls without code generation
• You need bidirectional communication (server calling client)
• You want automatic runtime validation

Features

• 🎯 Full TypeScript inference — Types flow automatically from server to client, no manual type definitions
• ✅ Automatic validation — Runtime validation using AJV ensures data matches your types
• 🔄 Bidirectional RPC — Server can call client actions with full type safety and validation
• 📡 Multiple transports — HTTP, streaming, WebSocket, and half-duplex—use what fits your needs
• 🚀 High performance — Fast validation, parallel execution, efficient streaming
• 🎨 Zero boilerplate — Simple API, works with any server framework
• 📁 File support — Built-in file upload/download across all transports
• 🛡️ Type-safe errors — Validation errors with detailed messages and type guards

Quick Start

1. Install

bun add ggtype
# or
npm install ggtype
# or
yarn add ggtype

2. Define your server

// server.ts
import { action, createRouter, m } from 'ggtype'

// Define an action with validation
const getUser = action(
  m.object({ id: m.string() }),
  async ({ params }) => {
    return { 
      id: params.id, 
      name: 'John Doe', 
      email: '[email protected]' 
    }
  }
)

// Create router
const router = createRouter({
  serverActions: { getUser },
})

export type Router = typeof router

// Use with any server
Bun.serve({
  port: 3000,
  async fetch(request) {
    return router.onRequest({ request, ctx: {} })
  },
})

3. Use in your client

// client.ts
import { createRouterClient, isSuccess } from 'ggtype'
import type { Router } from './server' // Type-only import

const client = createRouterClient<Router>({
  httpURL: 'http://localhost:3000',
})

// Call with full type safety
const result = await client.fetchActions.getUser({ id: '1' })

if (isSuccess(result)) {
  console.log('User:', result.data) // Fully typed!
} else {
  console.error('Error:', result.error?.message)
}

That's it! You get automatic validation, full TypeScript types, and a simple API.

Examples

For complete, runnable examples, see the examples/ folder:

• Hello World — Basic type-safe communication
• AI Tools — Bidirectional RPC (server calls client)
• Streaming — Real-time streaming updates
• WebSocket — Persistent bidirectional connections
• Duplex — Interactive bidirectional streaming

Core Concepts

Actions

Actions are type-safe functions with automatic validation:

const createUser = action(
  m.object({
    name: m.string(),
    email: m.string().isEmail(),
    age: m.number().min(18),
  }),
  async ({ params }) => {
    // params is fully typed and validated
    return { id: '123', ...params }
  }
)

Routers

Routers organize your actions and enable bidirectional RPC:

const router = createRouter({
  serverActions: { getUser, createUser },
  clientActions: { /* optional */ },
})

Clients

Clients provide type-safe access to your server actions:

const client = createRouterClient<Router>({
  httpURL: 'http://localhost:3000',
})

// Use proxy methods for automatic type narrowing
const result = await client.fetchActions.getUser({ id: '1' })

Streaming

Return streams from actions for real-time data:

// server.ts
const searchUsers = action(
  m.object({ query: m.string() }),
  async function* ({ params }) {
    // Yield results as they become available
    yield { id: '1', name: 'John', query: params.query }
    yield { id: '2', name: 'Jane', query: params.query }
  }
)

// client.ts
const stream = client.streamActions.searchUsers({ query: 'john' })

for await (const result of stream) {
  if (isSuccess(result)) {
    console.log('User:', result.data)
  }
}

Bidirectional RPC

The killer feature: Server can call client actions with full type safety and validation.

// server.ts
const clientActions = defineClientActionsSchema({
  showNotification: {
    params: m.object({ message: m.string() }),
    return: m.object({ acknowledged: m.boolean() }),
  },
})

type ClientActions = typeof clientActions

const updateUser = action(
  m.object({ id: m.string(), name: m.string() }),
  async ({ params, clientActions }) => {
    // Call client action with type safety
    const { showNotification } = clientActions<ClientActions>()
    const result = await showNotification?.({
      message: `User ${params.id} updated!`,
    })
    
    // Client response is validated automatically!
    if (result?.status === 'ok') {
      console.log('Acknowledged:', result.data.acknowledged)
    }
    
    return { success: true }
  }
)

const router = createRouter({
  serverActions: { updateUser },
  clientActions, // Enable bidirectional RPC
})

// client.ts
const client = createRouterClient<Router>({
  streamURL: 'http://localhost:3000', // Use stream/websocket for bidirectional
  defineClientActions: {
    showNotification: async (params) => {
      // params is validated automatically
      alert(params.message)
      // Return value is validated against schema
      return { acknowledged: true }
    },
  },
})

Key benefits:

• ✅ Full type safety on both sides
• ✅ Client responses are validated automatically
• ✅ Works with streaming, WebSocket, and duplex transports
• ✅ No manual type definitions needed

Transports

ggtype supports multiple transports. Choose what fits your needs:

| Transport | Use Case | Bidirectional RPC | |-----------|----------|-------------------| | httpURL | Simple request/response (REST-like) | ❌ | | streamURL | HTTP streaming, real-time updates | ✅ | | websocketURL | Persistent connections, chat, games | ✅ | | halfDuplexUrl | Interactive bidirectional streaming | ✅ |

Transport selection: When multiple URLs are provided, the client uses the first available in priority order (stream → websocket → http). No automatic downgrade.

const client = createRouterClient<Router>({
  streamURL: 'http://localhost:3000/stream',    // Tried first
  websocketURL: 'ws://localhost:3000/ws',       // Fallback
  httpURL: 'http://localhost:3000/http',        // Last resort
})

Server Integration

Works with any server framework. Just plug in onRequest or onMessage:

// Bun
Bun.serve({
  async fetch(request) {
    return router.onRequest({ request, ctx: {} })
  },
})

// WebSocket
Bun.serve({
  websocket: {
    message(ws, message) {
      router.onWebSocketMessage({
        ws,
        message: message as Uint8Array,
        ctx: {},
      })
    },
  },
})

// Elysia, Express, etc.
app.post('/api', async (req, res) => {
  const response = await router.onRequest({
    request: req,
    ctx: {},
  })
  return response
})

Error Handling

ggtype provides type-safe error handling:

import { isSuccess, isValidationError } from 'ggtype'

const result = await client.fetchActions.getUser({ id: '123' })

if (isSuccess(result)) {
  // TypeScript knows result.data exists
  console.log('User:', result.data)
} else {
  // TypeScript knows result.error exists
  if (isValidationError(result.error)) {
    console.error('Validation errors:', result.error.errors)
  } else {
    console.error('Error:', result.error.message)
  }
}

File Upload/Download

Built-in file support across all transports:

// Server: Receive files
const uploadImage = action(
  m.object({ title: m.string() }),
  async ({ params, files }) => {
    const imageFile = files?.get('file')
    // Process file...
    return { success: true }
  }
)

// Client: Upload files
const result = await client.fetchActions.uploadImage(
  { title: 'My Image' },
  { files: [imageFile] }
)

// Server: Return files
const getFile = action(
  m.object({ id: m.string() }),
  async ({ params }) => {
    return new File([content], 'document.pdf', {
      type: 'application/pdf',
    })
  }
)

// Client: Receive files
const result = await client.fetchActions.getFile({ id: '123' })
if (isSuccess(result)) {
  const file = result.data // File object
  const url = URL.createObjectURL(file)
}

Why ggtype vs alternatives?

vs REST/GraphQL

• ✅ Full type safety — End-to-end TypeScript inference
• ✅ Automatic validation — Runtime validation matches your types
• ✅ Bidirectional — Server can call client, not just client→server
• ✅ Less boilerplate — No manual API definitions or code generation

vs WebSocket libraries

• ✅ Type-safe — Full TypeScript inference for all messages
• ✅ Validation — Automatic validation on both sides
• ✅ Multiple transports — Not just WebSocket, choose what fits
• ✅ Simple API — Clean, consistent API across all transports

Model System

Rich validation system with TypeScript inference:

// Primitives
m.string(), m.number(), m.boolean(), m.date(), m.null()

// Files
m.file(), m.blob()

// Collections
m.array(model), m.object({ ... }), m.record(model)

// Unions
m.or(model1, model2), m.and(model1, model2), m.enums('a', 'b', 'c')

// Constraints
m.string().min(5).max(100).pattern(/^[A-Z]/)
m.number().min(0).max(100)
m.string().isEmail().isOptional()

// Custom validation
m.string().validate((value) => {
  if (value.length < 5) {
    return 'Must be at least 5 characters'
  }
})

All models are required by default. Use .isOptional() to make them optional.

API Overview

Router

createRouter(options)
  - serverActions: Record<string, Action>
  - clientActions?: ClientActionsSchema
  - responseTimeout?: number

router.onRequest(options)      // HTTP requests
router.onStream(options)       // HTTP streaming
router.onWebSocketMessage(options) // WebSocket messages

Client

createRouterClient<Router>(options)
  - httpURL?: string
  - streamURL?: string
  - websocketURL?: string
  - halfDuplexUrl?: string
  - defineClientActions?: Record<string, Function>
  - defaultHeaders?: Headers

client.fetch(params, options?)        // Multiple actions
client.stream(params, options?)       // Stream multiple actions
client.fetchActions.actionName(...)   // Single action (proxy)
client.streamActions.actionName(...)  // Stream single action (proxy)
client.startWebsocket()               // WebSocket connection
client.startDuplex()                  // Duplex connection

Actions

action(model, callback)
  - callback receives: { params, ctx, clientActions, files }
  - action.run(params) - Test actions directly (clientActions is optional)

defineClientActionsSchema(schema)

Utilities

isSuccess(result)           // Type guard for success
isError(result)             // Type guard for error
isValidationError(error)    // Type guard for validation errors
ValidationError             // Error class

📚 Full API Documentation — Complete reference with detailed examples and type definitions.

Advanced

Optional Parameters

const getUser = action(
  m.object({
    id: m.string(),
    includeEmail: m.boolean().isOptional(),
  }),
  async ({ params }) => {
    // params.includeEmail is optional
  }
)

Context

Pass context to actions:

const router = createRouter({
  serverActions: { getUser },
})

router.onRequest({
  request,
  ctx: { user: currentUser }, // Pass context
})

// In action
const getUser = action(
  m.object({ id: m.string() }),
  async ({ params, ctx }) => {
    const user = ctx?.user
    // Use context
  }
)

Response Timeout

const router = createRouter({
  serverActions: { getUser },
  responseTimeout: 30000, // 30 seconds
})

Testing Actions

You can test actions directly using action.run(). The clientActions parameter is optional—if not provided, it defaults to an empty object:

import { action, m } from 'ggtype'

const getUser = action(
  m.object({ id: m.string() }),
  async ({ params, ctx, clientActions }) => {
    // clientActions() is always available, even when not provided in tests
    const actions = clientActions()
    return { id: params.id, name: 'John' }
  }
)

// Test without clientActions (optional)
const result = await getUser.run({
  params: { id: '123' },
  ctx: { userId: 'user-1' },
  // clientActions is optional - defaults to empty object
})

// Test with custom clientActions
const resultWithClientActions = await getUser.run({
  params: { id: '123' },
  ctx: { userId: 'user-1' },
  clientActions: () => ({
    showNotification: async () => ({ status: 'ok', data: { acknowledged: true } }),
  }),
})

Performance

• ⚡ Fast validation — Uses AJV (faster than Zod)
• 🚀 Parallel execution — Multiple actions run in parallel
• 💾 Efficient streaming — Minimal memory overhead
• 📦 Lightweight — Minimal dependencies

Resources

• 📚 API Documentation — Complete API reference
• 📖 Examples — Runnable examples for all features
• 🐛 Issue Tracker — Report bugs or request features
• 💬 Discussions — Ask questions and share ideas

License

MIT License — see LICENSE file for details.